SOLUTION: bob fills a pool in 30 min, joe does it in 45 min frank takes 90 minutes - how may minutes will it take them all to fill the pool?

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Question 206789: bob fills a pool in 30 min, joe does it in 45 min frank takes 90 minutes - how may minutes will it take them all to fill the pool?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
they each fill a fraction of the pool based on their own times
___ the fractions sum to 1 (the whole pool)

let x="combined time"

x/30 + x/45 + x/90 = 1

multiplying by 90 (LCD) ___ 3x + 2x + x = 90 ___ 6x = 90 ___ x = 15